1. Field of the Invention
The present invention relates to optical communication equipment and, more specifically, to micro-electromechanical devices for use in such equipment.
2. Description of the Related Art
Optical communication equipment often employ micro-electromechanical systems (MEMS). A typical MEMS system may include an array of micro-machined mirrors, each mirror individually movable in response to an electrical signal. Such an array may be configured, e.g., as an optical cross-connect element. In operation, each mirror in the array receives a beam of light, for example, from an input optical fiber. The beam is reflected from the mirror and can be redirected to a different location, e.g., an output optical fiber, by rotating the mirror. More details on the principle of operation and methods of manufacture of MEMS devices including mirror arrays may be found, for example, in commonly assigned U.S. Pat. No. 6,201,631, the teachings of which are incorporated herein by reference.
One problem with prior art MEMS devices is related to electrostatic charge accumulation around defects, e.g., residual oxide, on the substrate layer and/or wafer. Electrostatic potentials generated by the accumulated charge may interfere with those generated by the actuating electrodes and therefore may affect the angle of rotation of the mirror. In addition, the amount of accumulated charge may change over time causing angle xe2x80x9cdrifting.xe2x80x9d Therefore, the performance of the device may be adversely affected.
An additional problem is related to manufacturing such devices. During fabrication, two pieces, e.g., wafers, forming the MEMS device need to be accurately aligned to properly position the electrodes with respect to the corresponding mirror. Such alignment may be difficult to achieve for relatively small mirrors and/or mirror arrays having a relatively large number of mirrors.
The present invention provides a shutter switch that may be fabricated using a single wafer, which alleviates the alignment problem associated with a two-piece prior art design. The switch has a movable mirror that is designed for in-plane motion. The mirror is connected to a drive shaft that can be moved, e.g., using one or more serpentine springs and a comb drive actuator. During operation, the mirror is in either one of two terminal positions. The mirror moves between the terminal positions in response to a voltage applied to the actuator. The springs and actuator are designed such that small voltage variations around the voltage values corresponding to the terminal positions do not substantially displace the mirror from those positions. As a result, any electrostatic charge accumulation will not result in significant drifting of the mirror. Multiple shutter switches may be arrayed in a single integrated structure.
According to one embodiment, the present invention is a shutter switch. The shutter switch has a stationary part, a movable part, and one or more springs connected between the stationary part and the movable part. The stationary part has a substrate and an immobile portion of an actuator rigidly connected to the substrate. The movable part is supported on the substrate and has a mirror, a shaft rigidly connected to the mirror, and a mobile portion of the actuator rigidly connected to the shaft. The actuator is configured to move the movable part relative to the stationary part in response to an electrical signal such that motion of the movable part generates mirror motion parallel to the plane of the substrate.
According to another embodiment, the present invention is a method of fabricating a movable structure supported on a substrate in an integrated device. The integrated device is formed in a wafer having at least three layers, wherein a second layer is formed over a first layer and a third layer is formed over the second layer. The first layer includes the substrate. According to the method, a first etching step is applied to form one or more openings in the third layer to expose portions of the second layer. A second etching step is applied to remove material from the second layer to detach the movable structure, wherein the movable structure is formed in the third layer and configured to move parallel to the plane of the wafer.